Commercial organisers tend to be too small for my liking, leaving the cable with a permanent coil after use. I found a credit card to be just the right length.
I cut out a notch at the top and bottom about 10mm deep. If you're wrapping a much longer cable than a set of earbuds or similar, make this deeper to keep the cable. There is no harm in doing 10mm and testing it first, as you can always cut it more!
Secondly, on the side right in the middle, cut a notch about 3 times wider and deeper than the cable you're going to use.
I bent the cutouts backwards to make a smooth corner for the cable, but if you want to store this card in your wallet, you'll want to cut the notches completely out so the card is perfectly flat afterwards. Your call.
It should look something like this: